How to tell when compost is ready to use
After a period of time composting in one bin, empty the bin and set aside the compost for a ‘curing’ period.
This will allow materials in the heap to finish the decomposition process at lower temperatures. Make sure the compost is moist and aerated by turning during the curing period, which can be as short as one month or as long as a year. While this batch of compost is curing, you can start adding materials to the compost bin again for the active composting process.
When the compost is ready depends on what it is being used for. Unfinished compost, where you can still recognise bits of what you originally put in, like eggshells, can be used as a layer of mulch on the soil surface. This will gradually decompose and be digested by worms, which distributes the nutrients into the soil.
Unfinished compost can also be dug-in to condition garden soils in the autumn, so it finishes decomposing in the earth by spring.
If you want to use the compost for planting trees, as lawn top dressing or as soil conditioner during the growing season, it needs to be more mature. Finished compost is moist and crumbly, smells earthy and doesn't contain recognisable materials.
You can also make ‘compost tea’ from mature compost to feed your houseplants and seedlings. This can be done by soaking some compost in a cheesecloth bag until the water is the colour of weak tea.